Process for purifying gases



Dec, B, 3924,

J. A. SHAW PROCESS FOR PURIFYING GASES Original Filed Deo. 8, 1921 FEES/'7' SOD/q SOLl/T/O/V Patented Dec. 30, 1924.

UNITED STATES LSZGJZG PATENT OFFICE.

JOSEPH. A. SHAW, OF PITTSBURGH, QPENNSYLVANIA, ASSIGNOR TO THE KOPPERS COM- PANY, OF PITTSBURGH, PENNSYLVANIA., A CORPORATION 0F 'PENNSYLVANIA.

PROCESS FOR PURIFYING GASES.

Application led December 8, 1921, Serial No. 520,789. Renewed May 19, 1924.

Purifying Gases, of which the following is a specification.

This invention relates to the removal of hydrogen sulphideand other noxious constituents, such as hydrocyanic acid, from gases containing them. Objects of the in# vention are to effect an efficient purification of the gases by means of an absorbent liquidl which removes the noxious constituents,

combined with revivification of the absorbent li uid by subsequent treatment thaty removes su stantially all theabsorbed sulphur in a solid form, whereby the escape of noxious fumes into the atmosphere in the vicinity ofl the gas urifying plant is avoided.

In adldition to the generalobjects recited above, the invention has for further objects such other improvements or advantages in operation and results as are found to obtain in the processes and apparatusA hereinafter described or claimed.

In the accompanying drawing formino a part of this specification and showing, or

erred purposes of exemplification, a pre form and manner in which the invention may be embodied and practiced, but without limiting the claimed invention specifically to such illustrative instance:

The figure illustrates a diagrammatic representation of apparatus for carrying out the improved gas purifying process of' the present inv ,ntion.

In its present embodiment, the invention is applied to the purification of foul gases, such as coke oven gas. For convenience, the present description will be confined to this important application of the invention. Features of the invention are, however, readily susceptible of other valuable applications; consequently, the invention is not confined in its scope to the specific use and embodiment herein described as an-illustrative example.

In carrying out the invention, the gases, after the tar and ammonia have been removed, are brought into contact with an absorbent agent constituted of a purifying solution which is alkaline in reaction, 'for r example: a sdium carbonate solution. The

' finer pebbles, then concentration of the solution may be varied as-desired; in practice, a one to five per cent solution of sodium carbonate will be found satisfactory. The gases to be purified enter the bottomI of the scrubber or washer A, through a gas line 1 and discharge from the top of said scrubber through the purifiedgas line 2. The purifying' solution is delivered tothe top of the scrubber A through the solution line 3 and the solution containing the absorbed impurities discharges from the bottom of said scrubber through a line 4 into a fouled solution tank or sump 5. In the scrubber, the solution absorbs the hydrogen sulphide and other noxious constituents ofthe gases, forming soluble sulphide compounds, such as sodium hydrogen sulphide. Carbon dioxide, if present in the gas, is also absorbed.

In accordance with the invention, the resulting fouled solution from the absorber A, is regenerated byeffecting contact of such fouled solution with a bed of an iron compound having an affinity for sulphur.v A

suitable iron compound for this purpose is iron oxide. vThe apparatus for such regenerative treatment of the fouled solution is illustrated in. the accompanying drawing and consists of a sand filter B, of any of the ordinary types, such as are employed in water purification. A filter of this type is constituted essentially of a tank with supporting grids near the bottom. On the grids, a layer of coarse pebbles is laid, and on these,

low thegrids a number of perforated air pipes are provided. For the present purposes, a bed of iron oxide may be employed in place of the fine sand, or may be mixed with the sand. The fouled alkaline solution from the tank 5 is discharged onto the bed of iron-oxide by means of a spray, for example, and filters through the iron oxide coming into intimate contact with it. As a result of such filtration, the iron oxide is converted into iron sulphide, and concurrently the alkaline solution is regenerated. rThe regenerated alkaline solution is diseharged from the bottom of the filter and may be pumped through an aerating vessel if necessary, before being delivered to the storage tank 1l. The fresh solution is then ready to purify'more gas in the absorber or scrubber A..

In practice, it is preferable to employ a fine sand. Above or be-v throu h yline 1 6 into the return solutionhiie v10. yInthe operationof the system, when the bed of iron oxide in any one.

tank is :well Sulphided, 1the fouled liquor inlet is shut off, and the'air is turned on'a't the bottom. This aeration converts the liron sulphideto iron oxide and to free sulphur,

' Sothat the bed is ,ready to 'treat i further sorbed:

` absor quantities of fouled1liquor.

The chemical reactions taking place in the absorption stage may be.exemplified by the following equations: l

' (a) Absorption of hydrogen sulphide by sodium carbonate: v

Na2oo+n2s=NaHs+Nanoo- (b) Carbon dioxide, if present, is also ab- (c) Hydrocyanic acid, if present, is also bed v Na2CO3+HCN=NaCN+NaHCO3- The chemical reaction in the vfilters mayv be exemplified by the following equation Conversion of iron oxide to iron sulphide and regeneration of the alkali:

.FezOs-q-aNaHS-paNaHCOa:

The chemical reaction during aeration of theiron sulphide in the filters is substan-` tially as follows Oxidation of iron sulphide to iron oxide and vfree sulphur:

2Fe2s3+30i=2re2o+6s vBy aerating the clear alkaline liquor, sodium bicarbonate is converted to carbonate, according to the following equation:

v lhe invention' as hereinabove set forth' alkali to absorb sulphur from the gas; then bringing the solutiony containing the absorbed impurities into contact with a bed occurs in which sul hur is transferred from the alkali -'to the iron, withformation of iron sul hide; then'dischargino the rejuve- .natd alkali .Solution-,for empoyment for further gas purification; and sub]ecting the iron sulphide lin the bed to aeration to remove the sulphur and to restore the iron to a state for effecting further absorption of sulphur; substantially las specified.

42. The process'of purifying gases which consists in: passing the gas into Contact with an absorbent 'solution constituted of dis# solved alkaline sodium compound to absorb sulphur from thev gas; thenbringing the solution containing the absorbed impurities into contact with a bed of an iron compound, whereby a. reaction occurs in which sulphur is -transferrnd `from the vsodium compound to theiron, with formation of iron sulphide; then 'discharging 'therejuvenated sodium compound solution for employment for further gas purifica-tion; and subjecting `the iron sulphide in the bed to aeration to re- -move the sulphur and to restore the iron to 'astate for effecting further vabsorption of sulphur; substantially asl specified.

3. The process of purifylng gases which consists in: passing the gas into contact with an absorbent Vsolution constituted of dissolved sodium carbonate to absorb sulphur from the gas; then bringing the solution containing the absorbed impurities into contact with a bed of an iron compound, whereby a reaction occurs in 4which sulphur is transferred from the sodium carbonate to the iron, with formation of iron sulphide; then -discharging the rejuvenated sodium carbonate solution for employment for furtherv gas purification; and subjecting the iron sulphidein the bed to aeration to remove the sulphur and to restore the iron to a state for effecting further absorption of sulphur; substantially as specified.

4. The process of purifying gases which consists in: passing the gas into contact with an `absorbent solution constituted of dissolved alkali to absorb sul hur from the gas; then bringing the solution containin the 'absorbed impurities into contact witi a bed of iron oxide, whereby a reaction occurs in which sulphur is transferred from the alkali to the iron, with formationof iron sulphide; then discharging the rej uvenated Aalkali solution for employment for further gas purification; and subjecting the iron sulphide in the bed to aeration to remove the sulphur and to restore the iron to a state for effecting further absorption of sulphur; substantiall as s ecified.

J SEP l A. SHAW. 

